1. Field of the Invention
This invention relates to re-utilization of a used photographic processing solution, or economical use of a photographic processing solution. Particularly, it is concerned with a method for effectively re-utilizing a used photographic processing solution by removing therefrom substances which are eluted from a light-sensitive material in the photographic processing solution and which are harmful for photographic processings. More particularly it is concerned with a method for selectively removing from a used photographic processing solution those compounds having relatively high molecular weights, such as polymer compounds and surface active agents, which accumulate during photographic processings.
2. Description of the Prior Art
In forming images by processing an imagewise exposed photographic light-sensitive material, various processing solution may be required, such as a developer, a fixer, a stop solution, a bleaching solution, a bleachfixer, a hardening solution, a neutralizer, a post-bath solution, a stabilizer, etc.
Processing solutions which have been used in development processing steps or which overflow processing vessels when such vessels are replenished, depending upon the particular process of the developing processing, have hitherto been disposed as a used processing solution, either as is or after being processed so as not to cause environmental pollutions.
These used processing solutions, however, still contain a large amount of processing components which have not been consumed during the processing. Therefore, the disposal of such used processing solusions is not preferred with respect to the effective utilization of resources, and it is disadvantageous from an economic viewpoint. Additionally, the application of such treatments so as to prevent environmental pollution results in increases in investment and overall production costs.
A method is known in which a processing solution that has been used for processing or an overflow solution from a processing vessel due to replenishment during the processing (hereinafter generically referred to as a "used solution") is reused after the removal of those components unnecessary or harmful with repect to the processing, and, if necessary, after replenishment of those components in which the solution is deficient.
The components which accumulate in the overflow solution and which are unnecessary or are harmuful with respect to processing include oxidation products of a developing agent, preservative, hydrogen ions, water-soluble salts, e.g., halogen ions (which are eluted from a light-sensitive material), surface active agents, water-soluble polymer compounds, dyes and other water-soluble additives. For example, the oxidation product of the developing agent in the processing solution causes fog, the other salts change photographic performance, and the surface active agents not only change photographic performance, but also render the processing solution subject to bubble formation, causing various hindrances during the processing. Of these components, halogen ions exert the most severe influences on the photographic performance.
As a method of removing such halogen ions from the photographic processing solution, an ion exchange resin method and an ion exchange membrane electrophoresis method are known.
In the ion exchange resin method, it is difficult to keep the amount of halogen ions being removed at a constant level, since the ion exchange capability of the ion exchange resin decreases with the use thereof. This makes it difficult to keep the photographic performance at a constant level. Furthermore, this method removes developing agents, such as hydroquinones and the like, which are relatively expensive and are necessary for re-use of the developing solution.
In accordance with the ion exchange membrane electrophoresis method, it is relatively easy to control the amount of halogen ions being removed, since the amount attains equilibrium after a certain period of time, although it abruptly changes at the beginning of the electrophoresis. Moreover, almost no developing agents are removed. It is, therefore, preferred to employ ion exchange membrane electrophoresis for the removal of halogen ions from the photographic processing solution.
However, while the ion exchange membrane electrophoresis method is effective for removing the halogen ions from the processing solution, it has the disadvantage that the efficiency of electrophoresis decreases with the repeated uses thereof. When the processing solution which has been used for processing a light-sensitive material is subjected to electrophoresis, the current efficiency, in particular, markedly decreases. At this point, the electrophoresis method cannot be used for the removal of salts such as halogen compounds and the like in the processing solution.
For the removal of those components which exert adverse influences on the electrophoresis method, various methods have hitherto been proposed, including a method as described in Japanese patent application (OPI) No. 146236/77 (the term "OPI" as used herein refers to a "published unexamined Japanese patent application") wherein a waste developer is brought into contact with a chelate resin and/or a week acidic cation exchange resin to control the formation of floating materals, a method as described in Japanese patent application (OPI) No. 46732/78 wherein a colored developer is brought into contact with a polymeric substance to remove the oxidation product of a developing agent and its derivatives, and a method as described in Japanese patent application (OPI) No. 19741/79 wherein a waste developer is brought in contact with an anion exchange member to remove colored substances in the waste developer.
Even if the methods as described above are applied prior to the electrophoresis of the used photographic processing solution, a gradual descrease in the efficiency of electrophoresis often occurs in practical operation, interfering with the continuation of the electrophoresis.